Field of the Invention
The invention relates to a process for producing a highly purified food ingredient from the extract of the Stevia rebaudiana Bertoni plant and its use in various food products and beverages.
Description of the Related Art
Sugar alternatives are receiving increasing attention due to the awareness of many diseases associated with the consumption of high-sugar foods and beverages. However, many artificial sweeteners such as dulcin, sodium cyclamate and saccharin have been banned or restricted in some countries due to concerns about their safety. As a result, non-caloric sweeteners of natural origin are becoming increasingly popular. The sweet herb Stevia rebaudiana Bertoni produces a number of diterpene glycosides which feature high intensity sweetness and sensory properties superior to those of many other high potency sweeteners.
The above-mentioned sweet glycosides, have a common aglycon, steviol, and differ by the number and type of carbohydrate residues at the C13 and C19 positions. The leaves of Stevia are able to accumulate up to 10-20% (on dry weight basis) steviol glycosides. The major glycosides found in Stevia leaves are rebaudioside A (2-10%), stevioside (2-10%), and rebaudioside C (1-2%). Other glycosides such as rebaudioside B, D, E, and F, steviolbioside and rubusoside are found at much lower levels (approx. 0-0.2%).
Two major glycosides—stevioside and rebaudioside A (reb A), were extensively studied and characterized in terms of their suitability as commercial high intensity sweeteners. Stability studies in carbonated beverages confirmed their heat and pH stability (Chang S. S., Cook, J. M. (1983) Stability studies of stevioside and rebaudioside A in carbonated beverages. J. Agric. Food Chem. 31: 409-412.)
Steviol glycosides differ from each other not only in their molecular structures, but also by their taste properties. Usually stevioside is found to be 110-270 times sweeter than sucrose, rebaudioside A between 150 and 320 times sweeter than sucrose, and rebaudioside C between 40-60 times sweeter than sucrose. Dulcoside A is 30 times sweeter than sucrose. Rebaudioside A has the least astringent, the least bitter, and the least persistent aftertaste, thus possessing the most favorable sensory attributes in major steviol glycosides (Tanaka O. (1987) Improvement of taste of natural sweetners. Pure Appl. Chem. 69:675-683; Phillips K. C. (1989) Stevia: steps in developing a new sweetener. In: Grenby T. H. ed. Developments in sweeteners, vol. 3. Elsevier Applied Science, London. 1-43.) The chemical structure of rebaudioside A is shown in FIG. 1.
Methods for the extraction and purification of sweet glycosides from the Stevia rebaudiana plant using water or organic solvents are described in, for example, U.S. Pat. Nos. 4,361,697; 4,082,858; 4,892,938; 5,972,120; 5,962,678; 7,838,044 and 7,862,845.
However, even in a highly purified state, steviol glycosides still possess undesirable taste attributes such as bitterness, sweet aftertaste, licorice flavor, etc. One of the main obstacles for the successful commercialization of stevia sweeteners are these undesirable taste attributes. It was shown that these flavor notes become more prominent as the concentration of steviol glycosides increases (Prakash I., DuBois G E., Clos J. F., Wilkens K. L., Fosdick L. E. (2008) Development of rebiana, a natural, non-caloric sweetener. Food Chem. Toxicol., 46, S75-S82.).
Rebaudioside B (CAS No: 58543-17-2), or reb B, also known as stevioside A4 (Kennelly E. J. (2002) Constituents of Stevia rebaudiana In Stevia: The genus Stevia, Kinghorn A. D. (Ed), Taylor & Francis, London, p. 71), is one of the sweet glycosides found in Stevia rebaudiana. Sensory evaluations show that reb B was approximately 300-350 times sweeter than sucrose, while for reb A this value was approximately 350-450 (Crammer, B. and Ikan, R. (1986) Sweet glycosides from the Stevia plant. Chemistry in Britain 22, 915-916, and 918). The chemical structure of rebaudioside B is shown in FIG. 2.
It was believed that reb B forms from the partial hydrolysis of rebaudioside A during the extraction process (Kobayashi, M., Horikawa, S., Degrandi, I. H., Ueno, J. and Mitsuhashi, H. (1977) Dulcosides A and B, new diterpene glycosides from Stevia rebaudiana. Phytochemistry 16, 1405-1408). However, further research has shown that reb B occurs naturally in the leaves of Stevia rebaudiana and is currently one of nine steviol glycosides recognized by FAO/JECFA (United Nations' Food and Agriculture Organization/Joint Expert Committee on Food Additives) in calculating total steviol glycosides' content in commercial steviol glycoside preparations (FAO JECFA (2010) Steviol Glycosides, Compendium of Food Additive Specifications, FAO JECFA Monographs 10, 17-21).
Only a few methods are described in literature for preparing reb B.
Kohda et al., (1976) prepared reb B by hydrolysis of reb A with hesperidinase. Reb B was also prepared by alkaline saponification of reb A. The said saponification was conducted in 10% potassium hydroxide-ethanol. The solution was acidified with acetic acid, and extracted with n-butanol. The butanol layer was washed with water and concentrated at low temperature in vacuo. The residue was crystallized from methanol to give reb B. (Kohda, H., Kasai, R., Yamasaki, K., Murakami, K. and Tanaka, O. (1976) New sweet diterpene glucosides from Stevia rebaudiana. Phytochemistry 15, 981-983). The described processes might be suitable for laboratory scale preparation of reb B, but are not suitable for any large scale or commercial reb B preparation.
Ahmed et al., used mild alkaline hydrolysis of reb A to prepare reb B. According to the described procedure, reb A was hydrolyzed to reb B by refluxing with 10% aqueous KOH at 100° C. for 1 hr. After neutralization with glacial acetic acid, the precipitated substance was recrystallized twice from methanol (Ahmed M. S., Dobberstein R. H., and Farnsworth N. R. (1980) Stevia rebaudiana: I. Use of p-bromophenacyl bromide to enhance ultraviolet detection of water-soluble organic acids (steviolbioside and rebaudioside B) in high-performance liquid chromatographic analysis, J. Chromatogr., 192, 387-393).
The use of methanol as recrystallization media as described in the literature will require its subsequent removal from the product. It is noted that handling of toxic substances such as methanol requires specialized manufacturing installations and, when applied in food processing, sophisticated food safety measures.
It is also noted that no significant work has been conducted to determine the potential of reb B as a sweetener or food ingredient. Moreover, reb B is often viewed as process artifact and unnecessary impurity in commercial steviol glycosides preparations. No significant evaluation of the influence of reb B on the overall taste profile of steviol glycoside preparations has been conducted.
The water solubility of reb B is reported to be about 0.1% (Kinghorn A. D. (2002) Constituents of Stevia rebaudiana In Stevia: The genus Stevia, Kinghorn A. D. (Ed), Taylor & Francis, London, p. 8). In many food processes where highly concentrated ingredients are used, a highly soluble form of reb B will be necessary.
Considering the facts mentioned above, there is a need to evaluate reb B as a sweetener and food ingredient and to develop a simple and efficient process for food grade reb B preparations suitable for food and other applications.
It is further noted that by having a carboxyl group in the molecule makes it possible for reb B to exist in the forms of various carboxylate salts. Prior to this invention, it is not believed that different carboxylate salt form of reb B had been prepared or evaluated for their impact on taste profiles.
Within the description of this invention we will show that, when applied in specific manner, carboxyate salts of reb B may impact the taste profile and offer significant advantages for the use of stevia sweeteners in various applications.